[tz] Ministry of Digital Development and Communications, the Government of Mongolia

Paul Eggert eggert at cs.ucla.edu
Tue Sep 19 21:15:31 UTC 2023

On 2023-09-19 01:00, fr via tz wrote:
> The Government of Mongolia is planning to switch to the regular summer time from 22-26 March, 2024. Currently, the discussions are made within the Government as well as at the Parliament. We expect that final decision will be made in the October. Therefore, is it possible to arrange the switching process in the next 5 months? Is there any extraordinary cases like us or not? Or shall we make our changes in the September 2024?

Thank you for letting us know.

If the Mongolian government publishes its official decision in October 
and notifies us, we can generate a new TZDB release quickly. However, it 
will take some months for this release to trickle out to cell phones, 
computers, and other devices, because many intermediaries check TZDB 
data before redistributing it, and because users often wait for some 
time before installing updates. This is why we suggest a year's notice 
for changes. (Even a year's notice is not perfect, as some devices will 
never be updated, but one cannot wait forever.)

With five months' notice many devices will be updated, but it is hard to 
predict how many. So it is a judgment call as to whether five months is 
enough for Mongolia. Although the TZDB project suggests twelve months' 
notice, this is not a strict requirement.

Although it is not clear from your email, I guess that the government of 
Mongolia plans to switch its time zone permanently, so that clocks in 
Ulaanbaatar would move forward one hour on (say) March 29, 2025 at 02:00 
local time, and that no further clock adjustments would occur 
afterwards. That is, Ulaanbaatar would simply change its time zone from 
8 to 9 hours ahead of UTC on a designated date and time.

If my guess is correct, it might be better for Mongolia to change its 
clocks in spring and not in autumn, as moving clocks forward in autumn 
works against the normal pattern of sunsets coming earlier in autumn.

Also, it would make sense to review "Costs and benefits of time shifts", 
which summarizes scientific reviews of whether and when to change time 
zones. Please see:


Finally, I echo Nick's request in 
<https://mm.icann.org/pipermail/tz/2023-September/033044.html> for any 
information your government has about past time changes and boundaries 
between time zones in Mongolia, so we can correct any mistakes in TZDB 
concerning your country.

Thank you.

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